Asymmetrically conductive transmission system using adjacent dielectric plate to concentrate field in gyromagnetic plate



Oct. 1963 H. G. BELJERS ETAL 3,

ASYMMETRICALLY CONDUCTIVE TRANSMISSION SYSTEM USING ADJACENT DIELECTRIC PLATE To CONCENTRATE FIELD IN GYROMAGNETIC PLATE Filed Nov. 9, 1955 INVENTORS HUGO GERRIT BELJERS LOUIS VAN DER Ki NT United States Patent 3,105,946 ASYMMETRHZALLY CDNDUCTWE TRANdMIS- SEON SYSTEM UING ADEACENT DELECTRIC PLATE T0 CUNCENTRATE FELD IN GYRG- MAGNETIC PLATE Hugh Gerrit Beljers and Louis van der Kint, Eindhoven,

Netherlands, assignors, by mesne assignments, to North American Philips (Iompany, Inc, New York, N.Y., a

corporation of Deiaware Filed Nov. 9, 1955, Ser. No. 545,882 Claims priority, application Netherlands Nov. 19, 1954 5 Claims. (til. 333-242) The present invention relates to asymmetrically conductive transmission systems, or transmission systems in which electromagnetic waves are passed in one direction and are not passed in the opposite direction.

Such a system is known in which, in a waveguide at a point at which the magnetic vector of a wave to be passed or to be blocked, respectively, is circularly polarized, a strip of high-frequency magnetic material, for example, ferrite, is positioned. The material, in the direction at right angles to the plane of rotation of the said magnetic vector, is polarized in a degree sufiicient to produce ferromagnetic resonance.

In the transmission system in accordance with the present invention, a plate of dielectric material is positioned on one side of the magnetic strip having a dielectric constant at least substantially equal to the square root of the dielectric constant of the magnetic material, and a thickness at least substantially equal to one-fourth the velocity of light divided by the square root of the dielectric constant of the dielectric material multiplied by the frequency of the waves.

Experiments have shown that the arrangement of the present invention permits a substantially great increase of the ratio between the blocking coelficient and the pass coefiicient.

In order that the invention may be readily carried into eiiect, it will now be described more fully with reference tothe accompanm'ng drawing, wherein the single FIGURE is a cross-sectional diagram of an embodiment of the arrangement of the present invention.

In the figure, a rectangular waveguide 1 has a size which, in the x-direction, is equal to a and which, in the y-direction, is equal to b. Longitudinally magnetic waves of the type H can propagate in the Waveguide in the z-direction, that is, at right angles to the plane of the drawing. The magnetic vector components H and H can be represented by while the component H is equal to zero. Here p represents the propagation constant, which is where w is the angular frequency of the waves, c is the velocity of light, a is the size of the waveguide in the direction of the x-axis, and B is a constant. In the for- 3 ,lli5,iiifi Patented Oct. 1, 1963 mulas tor H and H the upper sign applies to waves propagating in the direction of the positive z-laxis and the lower sign to waves in the opposite direction. The vector component H at all points exhibits a phase difference with respect to the component H At the point at which tan i a. pa.

the absolute values of these components are equal, and consequently an exactly circularly polarized magnetic rotating field is produced, the plane of rotation of the magnetic vector for waves propagating in the direction of the positive z-axis is opposite to that for waves in the opposite direction. At the abovementioned point in the wave-guide '1 a thin strip 2, of ferrite, is arranged. The magnetic strip 2 extends through a certain distance in the direction of the axis of the waveguide and preferably is tapered at the ends in order to avoid undesirable reflections. The magnetic strip 2 is polarized by a magnetic field H in the y-direction, that is, in the direction at right angles to the plane of rotation of the magnetic vector. Thus, when there are no waves in the Waveguide, the magnetic spin of the electrons in the magnetic material of the strip 2 will be directed along the ya-axis.

As is well known, in a polarized high frequency magnetic material which is arranged in a linearly polarized alternating magnetic field at right angles to the direction of polarization, a precession of the magnetic electron spin will be produced in a predetermined direction of rotation about the direction of polarization. When the magnetic material is arranged in a circularly polarized magnetic rotating field, the sense of rotation of which is equal to that of the precession movement, the componentsat right angles to one another of this rotating field will be additive to one another. As is cturther well known, at a predetermined value of the polarizing field, dependent upon the frequency or the rotating field, a ferromagnetic resonance is produced with a resultant very high absorption of the electromagnetic wave.

When the sense of rotation of the magnetic rotating field is opposite to that of the precession movement, the rotating field components at right angles to one another will oppose each other so that there is no ferromagnetic absorption. A very slight absorption persists, which may, for example, be due to dielectric losses :and magnetic losses caused by imperfection of the magnetic material and to the finite thickness of the magnetic strip. Waves propagating in the waveguide in a direction [for which the sense of rotation of the magnetic vector at the point of the magnetic strip 2 is opposite to that of the precession movement will consequently be passed substantially unimpeded, whereas waves in the opposite direction are highly damped. The attenuation in the first case may be equal to about 1.5 decibels and the attenuation in the second case may be equal to about 20 decibels.

Experiments have shown that this ratio can be mater-ially improved by positioning on the magnetic strip 2 a plate 3 of dielectric material, the dielectric constant of which is equal to the square root of the dielectric constant electric plate 3, in other words, approximately equal to one-fourth the Wavelength of the waves in the dielectric plate 3. An explanation of this phenomenon might be that without the provision cf the dielectric plate 3 a certain reflect-ion of the Waves from the surface of the magnetic strip 2 occurs, so that a certain amount of wave energy can escape through the space between the righthand side wall of the strip 2 and the right-hand side-Wall of the waveguide 1. Due to the provision of the dielectric plate 3, which behaves as a quarter wavelength transformer, there will be better matching of the said space and the magnetic strip 2, so that the wave energy is concentrated to a higher degree on the magnetic strip 2 and the reflection from the surface of said magnetic strip is highly reduced. This arrangement insures, as tests have shown, an attenuation of more than 50 decibels in the Waves propagating in the non-conductive direction. In addition, it was found that the provision of a dielectric plate at the opposite side of the magnetic strip 2, that is, at the side remote from the axis of the waveguide, produces little effect or may even produce a reverse effect.

The same arrangement may be used with other types of waves in a waveguide of rectangular or circular crosssection. In the latter case with the type H for example, a phase shift of 90 is produced between the radial and axial components of the magnetic field and the absolute values of these components at two predetermined distances from the waveguide axis are equal. At one of the said distances a ferrite cylinder may be positioned and polarization may be produced by means of a direct current sent through a conductor arrangd in the axis of the waveguide, which conductor does not interfere with the field since the axial component of the electric vector of the wave type H is Zero. Consequently, the magnetic lines of force are circles about the axis. This asymmetrically conductive transmission system can, in accordance with the invention, be improved by the provision of a cylinder made of dielectric material, the dielectric constant or which is equal to the square root of the dielectric constant of the ferrite, and the thickness of which is equal to one-fourth the wavelength for waves Within the dielectric material. This dielectric cylinder is positioned inside or outside the ferrite cylinder according as the radius of the latter has the maximum or the value at which the magnetic vectors are equal to one another. For this purpose a cylinder made of quartz, for example, may be utilized.

It is understood that the invention is not limited to the netic vector of a wave insaid system is circularly polarized,

a strip of ferromagnetic material which exhibits the gyromagnetic effect positioned at said point within said waveguide, said ferromagnetic material being polarized in a degree sufficient to produce ferromagnetic resonance in a direction at right angles to the plane of rotation of said magnetic vector, and a plate of dielectric material positioned on one side of said ferromagnetic material strip, said plate having a dielectric constant substantially equal to the square root of the dielectric constant of said ferromagnetic material and a thickness substantially equal to one fourth the velocity of light divided by the square root of the dielectric constant of said dielectric material multiplied by the frequency of the waves in said system.

2. An asymmetric-ally conductive transmission system in which in a Waveguide at a point at which the magnetic vector of a wave which is to be passed or to be blocked respectively is circularly polarized, a strip of ferromagnetic material which exhibits the gyromagnetic effect is positioned, which material in the direction at right angles to the plane of rotation of the said magnetic vector is polarized in a degree sufficient to produce ferromagnetic resonance, comprising a plate of dielectric material positioned on one side of said ferromagnetic material strip, the dielectric constant of said dielectric plate being at least substantially equal to the square root of the dielectric constant of said ferromagnetic material, and the thickness of said dielectric plate being at least substantially equal'to one-fourth the velocity of light divided by the square root of the dielectric constant of said dielectric material multiplied by the frequency of the waves in said system.

3. An asymmetrically conductive transmission system comprising a wavegulide having a point at which the magnetic vector of a wave in said system is circularly polarized, a strip of ferromagnetic material which exhibits the gyrcmagnetic effect positioned at said point within said waveguide, said ferromagnetic material being polarized in a degree sufficient to produce ferromagnetic resonance in a direction at right angles to the plane of rotation of said magnetic vector, and a plate of nonmagnetic dielectric material positioned substantially adjacent one side of said ferromagnetic material strip, said plate having a thickness substantially equal to one-fourth the wavelength of the waves in the said plate.

4. An asymmetrically conductive transmission system comprising a wave-guide having a point at which the magnetic vector of a wave in said system is circularly polarized, a strip of ferromagnetic material which exhibits the gyromagnetic effect positioned at said point within said waveguide, said ferromagnetic material being polarized in a degree sufiicient to produce ferromagnetic resonance in a direction at right angles to the plane of rotation of said magnetic vector, and a plate of dielectric material positioned on one side of said ferromagnetic material strip, said plate having a dielectric constant substantially equal to the square root of the dielectric constant of said ferromagnetic material and a thickness in the transverse the wave-s in said system.

5. A nonreciprocal dominant mode electromagnetic wave energy component comprising a section of rectan gular waveguide for said energy having conductive top and bottom wide walls and conductive narrow side walls, a slab of magnetically polarizable material having a :given high dielectric constant and exhibiting gyromagnetic effects in the presence of said energy extending within said section parallel to and at unequal distances hrom rmpective narrow side walls, said slab having a transverse dimension parallel to said Wide walls that extends through a first region in which said energy has transverse and longitudinal magnetic field components of equal amplitude into the region on each side of said first region in which said components are of slightly different amplitude, means for applying a magnetic biasing field to said gyromagnetic slab in a direction transverse to the direction of energy propagation through said guide, solely a single solid self-supporting slab of nonmagnetic high dielectric-constant dielectric material having a rectangular transverse cross section with a thickness parallel to said wide walls at least as great as said transverse dimension of said gyromavgnetic slab extending solely at the guide centerline side of and in contiguous relationship with said gyromagnetic slab, and a relatively low dielectric-constant dielectric medium filling the major portion of theremainder of the transverse cross section of said sec-tion,,the

dielectric constant of said nonmagnetic slab having a References Cited in the file of this patent UNITED STATES PATENTS Bloch et a l. Feb. 22, 1955 (Other references on following page) UNITED STATES PATENTS Freen beng Jan. 23, 1951 Weber Jan. 17, 1956 Driscoll Apr. 10, 1956 Hewitt -May 8, 1956 Fox Apr. 2, 1957 Iversen Mar. 10', 1959 Davis et al Oct. 20, 1959 5 OTHER REFERENCES Kale-s et aL: A Nonreclprocal Microwave Component, Journal of Applied Physics, vol. 24, No. 6, June 1953, pages 816-17.

5 Sullivan et al.: Journal of Applied Physics, vol. 26, No.

10, October 1955, pages 1282-83.

Fox et 31.: Bell System Technical Journal, vol. 34, No. 1, January 1955, pages 26-32, 49-5 2 and 61-65.

Weiss: IRE Transactions on Micnowave Theory and 10 Techniques, October 1956, pages 240-243.

UNITED STATES PATENT QFFICE CERTIFICATE OF CORRECTION Patent No: 3, lO5 946 October 1 v 1963 Hugo Gerrit Beljers et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant line 1 and in the heading to the printed specification line 6, for "Hugh Gerrit Beljers", each occurrence read Hugo Gerrit Beljers column 3 line 67 and column 4 lines 9 and 39 after "system", each occurrence insert W said dielectric material being disposed only on the side of said strip toward the longitudinal axis of said waveguide same column 41 line 22 after "plate" insert 9 said dielectric material being disposed only on the Side of said strip toward the longitudinal axis of said waveguide a Signed and sealed this 5th day of May 1964. (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

5. A NONRECIPROCAL DOMINANT MODE ELECTROMAGNETIC WAVE ENERGY COMPONENT COMPRISING A SECTION OF RECTANGULAR WAVEGUIDE FOR SAID ENERGY HAVING CONDUCTIVE TOP AND BOTTOM WIDE WALLS AND CONDUCTIVE NARROW SIDE WALLS, A SLAB OF MAGNETICALLY POLARIZABLE MATERIAL HAVING A GIVEN HIGH DIELECTRIC CONSTANT AND EXHIBITING GYROMAGNETIC EFFECTS IN THE PRESENCE OF SAID ENERGY EXTENDING WITHIN SAID SECTION PARALLEL TO AND AT UNEQUAL DISTANCE FROM RESPECTIVE NARROW SIDE WALLS, SAID SLAB HAVING A TRANSVERSE DIMENSION PARALLEL TO SAID WIDE WALLS THAT EXTENDS THROUGH A FIRST REGION IN WHICH SAID ENERGY HAS TRANSVERSE AND LONGITUDINAL MAGNETIC FIELD COMPONENTS OF EQUAL AMPLITUDE INTO THE REGION ON EACH SIDE OF SAID FIRST REGION IN WHICH SAID COMPONENTS ARE OF SLIGHTLY DIFFERENT AMPLITUDE, MEANS FOR APPLYING A MAGNETIC BIASING FIELD TO SAID GYROMAGNETIC SLAB IN A DIRECTION TRANSVERSE TO THE DIRECTION OF ENERGY PROPAGATION THROUGH SAID GUIDE, SOLELY A SINGLE SOLID SELF-SUPPORTING SLAB OF NONMAGNETIC HIGH DIELECTRIC-CONSTANT DIELECTRIC MATERIAL HAVING A RECTANGULAR TRANSVERSE CROSS SECTION WITH A THICKNESS PARALLEL TO SAID WIDE WALLS AT LEAST AS GREAT AS SAID TRANSVERSE DIMENSION OF SAID GYROMAGNETIC SLAB EXTENDING SOLELY AT THE GUIDE CENTERLINE SIDE OF AND IN CONTIGUOUS RELATIONSHIP WITH SAID GYROMAGNETIC SLAB , AND A RELATIVELY LOW DIELECTRIC-CONSTANT DIELECTRIC MEDIUM FILLING THE MAJOR PORTION OF THE REMAINDER OF THE TRANSVERSE CROSS SECTION OF SAID SECTION, THE DIELECTRIC CONSTANT OF SAID NONMAGNETIC SLAB HAVING A VALUE WHICH IS CLOSER TO THE DIELECTRIC CONSTANT OF SAID GYROMAGNETIC SLAB THAN TO THE DIELECTRIC CONSTANT OF SAID FILLING MEDIUM. 